The invention relates to the field of optical networks.
Optical networks typically utilize a plurality of optical sources, typically lasers, to generate optical carriers which are typically modulated with information at a transmitting station, transmitted on one or more optical waveguides (typically optical fiber), and subsequently demodulated at a receiving station. Two or more optical carriers of differing wavelengths xcexi are typically multiplexed onto an optical waveguide, transmitted along the optical waveguide, and de-multiplexed at another location, at which location one or more modulated optical carriers is demodulated and the information delivered to its destination.
FIG. 1 (prior art) is a block diagram of a ring Optical Add/Drop Multiplexed (OADM) network 100, comprising a plurality of add/drop nodes 102. FIG. 2 (prior art) is a block diagram of a linear Optical Add/Drop Multiplexed (OADM) network 200, comprising a plurality of add/drop nodes 202. A typical add/drop node 300 is depicted in FIG. 3 (prior art).
A multiplexed input signal 302 comprising a plurality of modulated respective optical carriers (also referred to as wavelengths herein) each carrier comprising a substantially single respective wavelength xcexi, i.e., a substantially pure single wavelength beam, passes through an optical amplifier 304, and into a separating device 306, typically a de-multiplexing device, that separates the xe2x80x9cthroughxe2x80x9d wavelengths 308 from the xe2x80x9cdropxe2x80x9d wavelengths 310. The drop wavelengths 310 are directed to a device 312 where they are de-multiplexed, and each wavelength is output onto an optical waveguide 314, which waveguide is typically optical fiber. Each of the drop wavelengths 310 is demodulated in a respective receiver 316, the respective receiver 316 then passing the information as a result of demodulation, on to its respective destination. The information received at receiver 316 is also, in parallel fashion, channeled to an input 322 (labeled Add signal #1) of a modulator 320, where the information modulates a new beam originating from a source 318 whose wavelength is typically identical to the carrier of the respective drop wavelength (in this case, xcex1). Each information channel to be modulated typically requires a separate laser source, as typically a laser source emits a single carrier wavelength. Laser sources used in optical networks tend to be costly items; therefore it would be advantageous to reduce the number of sources, e.g., 318, typically lasers, needed to operate the add/drop node 300.
FIG. 9 is a block diagram of a Passive Optical Network (PON), comprising a Host Digital Terminal (HDT) 902, which in turn typically comprises a plurality of Host Digital Terminal Passive Optical Network Terminal Modules (HPTM) 904, and typically a plurality of Optical Network Units (ONU) 906. Typically each of the Optical Network Units (ONU) 906 comprises an optical source, typically a laser, which, in the ONU""s transmit mode, generates a carrier wavelength xcexi that is modulated in the ONU before being output. As indicated above, optical sources, typically lasers, used in optical networks tend to be costly items; if it were possible to eliminate the necessity for each ONU to comprise an optical source, the result would be advantageous, in that there would be a reduction in the overall number of optical sources required in order to operate the PON.
Methods and apparatuses are contemplated for sharing optical sources in an optical network, which typically reduces the number of optical sources needed to operate the optical network.